Field of the Disclosure
The present invention relates generally to a method to produce chemically prepared toners for use in electrophotography and more particularly to a method for preparing a chemically prepared toner using a crash cooling step wherein hot toner slurry is added to an external reactor containing a coolant comprised of previously cooled toner slurry in combination with cooled de-ionized water. The previously cooled toner slurry found in the coolant has the same toner composition as the incoming hot toner slurry. Also, the amount of the coolant in the external reactor is equivalent to the amount of incoming hot toner slurry.
Description of the Related Art
Toners for use in electrophotographic printers include two primary types, mechanically milled toners and chemically prepared toners (CPTs). Chemically prepared toners have significant advantages over mechanically milled toners including better print quality, higher toner transfer efficiency and lower torque properties for various components of the electrophotographic printer such as a developer roller, a fuser belt and a charge roller. The particle size distribution of CPTs is typically narrower than the particle size distribution of mechanically milled toners. The size and shape of CPTs are also easier to control than mechanically milled toners.
One process for preparing a CPT is by emulsion aggregation. Emulsion aggregation is carried out in an aqueous system resulting in good control of both the size and shape of the toner particles. The toner components typically include a polymer binder, one or more colorants and a release agent.
Known crash cooling processes for preparing a CPT by emulsion aggregation involve the addition of cooling water, in particular chilled water, following a toner rounding step and prior to filtration, in what is called a crash cooling step. A known crash cooling method adds an amount of cooling water that is equivalent to the amount of reactor batch of toner placed in an external reactor. This method of crash cooling unfortunately limits the quantity of toner that can be produced from a single reactor batch. In an alternate crash cooling method, the hot toner slurry is placed into an external reactor having an equivalent amount of de-ionized water that has been cooled from about 7° C. to about 25° C. Toners cooled by these crash cooling methods can have either non-uniform crystalline domains (adding cold water to hot toner slurry) or more uniform crystalline domains (adding hot toner to cold water). However, cooling of the toner by the above techniques requires an equivalent amount of de-ionized water and therefore uses a large quantity of cooled de-ionized water for making and cooling the toner. Another crash cooling method puts hot toner slurry into a reactor containing ice. Unfortunately, the crash cooling by this method results in non-uniform crystalline domains, and variability in the crystalline domains across the toner batch. As may be envisioned by adding hot toner slurry (for example 80° C.) to an ice bath would result in rapid cooling for the initial batch of toner and as the ice melts and temperature increases, the latter half of the toner batch would see a slower cooling rate. Accordingly, an alternate method to cool toner using a reduced amount of de-ionized water is preferred both in terms of being more cost effective and more environmentally friendly. Additionally, the crash cooling method of the present invention also increases overall productivity, by utilizing a small amount of a previous cooled batch of toner slurry as a coolant medium for the newer batches of toner being manufactured.